1. Field of the Invention
The present invention relates to a light-emitting element having an EL layer between a pair of electrodes. Further, the present invention relates to a light-emitting device using the light-emitting element.
2. Description of the Related Art
Since light-emitting elements having an EL layer between a pair of electrodes are self-emission elements, high visibility can be achieved, they can be suitably used for thinner devices in that backlights needed for liquid crystal display devices (LCDs) are unnecessary, and the viewing angle has no limits. Thus, display devices using light-emitting elements have attracted attention as an alternative to CRTs or LCDs and have been increasingly put into practical use. Furthermore, light-emitting elements are thin planar light sources, and fewer limitations are imposed on their shapes. Thus, lighting devices having light-emitting elements as light sources have been expected to find new applications, as well as to replace conventional lighting devices using filament lamps, incandescent lamps, LEDs, and the like.
In order to increase the luminance of a light-emitting element, the amount of current supplied to the light-emitting element is increased. However, a larger amount of current supplied to a light-emitting element accelerates the deterioration of an EL layer, which reduces the lifetime of the light-emitting element. In view of this, Patent Document 1 given below discloses a structure of a light-emissive element in which light-emissive units having light-emissive layers are stacked between an anode and a cathode and a charge generation layer is provided between the units. With this structure, the luminance of the light-emissive elements can be increased while an increase in the amount of current supplied to light-emissive layers is suppressed.